THE MEASUREMENT OF METAL IONS USING LAGERSTROEMIA SPECIOSA (L.) PERS. FLOWER EXTRACTS WITH DIGITAL IMAGE COLORIMETRY TECHNIQUES ON SMARTPHONES

Abstract

The anthocyanin is a ligand that forms complexes with metal ions, creating colored coordination compounds. These can be applied for qualitative analysis, and when combined with digital image colorimetry, they allow for quantitative measurement. Therefore, the objective of this study was to investigate the color change of the extract when tested with metal ions at varying concentrations, along with the digital image colorimetry technique. Anthocyanin was extracted from the flowers of the Lagerstroemia speciosa (L.) Pers. using deionized water. The total anthocyanin content was determined by the pH-differential method. The color change of the extract was tested with 12 types of metal ions: Aluminum ion, Cobalt (II) ion, Chromium (II) ion, Copper (II) ion, Ferrous (II) ion, Ferric (III) ion, Magnesium ion, Manganese (II) ion, Molybdenum (VI) ion, Nickel (II) ion, Lead (II) ion, and Zinc (II) ion, under pH 1-13. The intensity of the red, green, and blue (RGB) values was measured using the RGB Color Detector application. A standard concentration graph was created between the color intensity and the metal ion solution concentration, and the accuracy of the analysis was tested using the Paired t-test statistical method. The results revealed that the extract from the Lagerstroemia speciosa (L.) Pers. flowers was purple and absorbed light at the maximum wavelength (λ_max) of 550 nm. The total anthocyanin content was 1.81 mg CGE/100 g of FW. The extract exhibited clear color changes when tested with Cobalt (II) ion, Chromium (II) ion, Ferrous (II) ion, Ferric (III) ion, Molybdenum (VI) ion, and Zinc (II) ion. The R² values from the standard graphs of the digital image colorimetry technique for Ferrous (II) ion and Ferric (III) ion, derived from the red, green, and blue values, were all above 0.990. The accuracy test using the Paired t-test between the digital image colorimetry technique and spectrophotometry for Ferrous (II) ion and Ferric (III) ion analysis showed no significant difference at the 99% confidence level. This indicates that the method can be developed into a test kit for detecting or measuring the concentration of metal ions in environmental samples in the future.